Measure the length and height of your countertop edges, using a tape measure. Use these measurements to purchase enough snap-on metal trim pieces to fit your countertop length while also being of a sufficient height. Add about 10 percent to the length to allow for cutting the trim to fit snugly or to miter in order to cover corners.
Put on a pair of work gloves and safety goggles for protection. Measure the countertop again to make certain your measurements are accurate. When measuring, measure around outside edges, as you can place a bend in the trim at these points to keep the trim continuous. Mark a cutting line across the snap-on trim, using a grease pencil with a straightedge placed along the trim to keep your cutting line plumb. Mark marks along the trim at any outside corners as well. Use separate trim pieces where you find inside corners on your countertop. Cut the trim along the cutting lines, using a pair of tin snips. On the outside corner locations, cut the top and bottom edges of the trim where the trim fits over the top and bottom of the countertop when snapped in place.
Bend the trim into a 90-degree angle at the outside corner locations. The cut top and bottom edges of the trim will overlap. Cut the overlap pieces so they come together at a 45-degree angle to create a mitered edge that will fit flat against the top and bottom of your countertop at the corners.
Apply a bead of silicone caulk along the edge of the countertop. Place the trim on the countertop edge, and then press it in place until the trim is flat against the countertop edge, with the small trim edging pieces overlapping the top and bottom edges of the countertop. Place a second bead of caulk along the edge of the trim where it meets the laminate surface to prevent water from flowing beneath the trim. Smooth the caulk with a wet fingertip.
Install the two sections of an inside corner by making a 45-degree miter cut along the meeting edges, and then gluing both in place with the caulk.
Slide the metal trim backsplash trim down the rear of the countertop along the wall, with the overhanging section of the rim toward the countertop body. Slip the trim down the rear of the counter until the overhanging piece lies flat along the rear of the countertop. If the countertop was already glued to the wall, then use a putty knife to break the glued bond between the countertop and the wall by forcing the knife along the rear of the countertop against the wall before you place the metal trim backsplash.
Place a bead of caulk along the base of the backsplash trim to protect against moisture as well. Smooth the caulk in place with your wet fingertip, and then allow the glue and caulk 48 hours of drying time before you use the newly trimmed countertop.